Tube still



atented Jan. 18, 1938 ATENT TUBE s 1 Ralph M. Parsons, Mount Vernon, h10, Y'

or to The Ralph M. Parsons Company,

2 Claims.

This invention relates to furnaces and more particularly to tube stills for the treatment of hydrocarbon oils. y

An object of the invention is to provide a furnace for the above purpose which is cheap and simple in construction, efficient in operation and adaptable to variousv uses in oil refining and cracking plants.

Another object is to provide a furnace in which the tubes are arranged to absorb heat efciently, to protect and shield the furnace walls and to ltransfer heat to the liquid within the tubes at the maximum permissible rate.

Another object is to provide a furnace which may be altered by simple changes in connections to accommodate different types or grades of oil.

Another object is to provide a furnace that is adapted to operate as a cracking furnace or a combination cracking and reforming furnace 0r for other purposes which may arise in an oil rening plant.

Various other objects and advantages will be apparent as the nature of the invention is more fullyy disclosed.

Although the novel features which are believed to be characteristic of this invention will be point.- ed out more particularly in the claims appended hereto, the invention itself, as to its objects and advantages and the manner of its application, will be better understood by referring to the embodiments thereof disclosed in the accompanying drawing and more specifically described herein for purposes of villustration only.

In the drawing:

Fig. 1 isa vertical transverse section through a furnace constructed in accordance with this invention, showing the tubes in a conventional manner; and

Fig. 2 is a similar view showing a different embodiment of the invention.

In the various figures, like parts have ignated by like reference characters.

Specific terms are used herein for convenience of description but it is to be understood that they are to be interpreted as broadly as the state of the art will permit. 1

Y Referring to the drawing more in detail, the' invention is shown in Fig. 1 as applied to a furnace having a oor 9, side walls l0 and I0' and a center wall I-I separating the lower part of the furnace into a pair of combustion chambers l2 and i3. The walls I0, i0 and il are preferably arranged so that the combustion chambers l2 been desland i3 are rectangular in shape and are comparatively narrow.`

'I'he walls l0, l0 may be supported in any convenient manner, as by stays ld, and may be carrid upon a suitable foundation I5 through which air ducts i6 and fuel pipes l1 may extend. Each air duct i6 terminates at a burner 20 or 20 which may, for example, comprise a block of refractory material having a flared passage 2l formed therein, similar in shape to a Venturi tube. The fuel pipe l1 terminates in a jet 22 which is so disposed with respect to the passage 2l that the flow of fuel gas through said passage induces ythe required ow of air for combustion purposes through the duct I6. The flared passage 2l, in

addition to assisting the maintenance of the re# quired iiowof fuel gas and air, also provides an eicient mixing device for thoroughly mixing the air with the fuel whereby complete combustion. may be obtained without the addition ofsecondary air.

The burner 20 may be formed of a block of high grade refractory material but in order to reduce the cost thereof it is preferable to form the burner of a cheaper grade refractory and to line the passage 2l atthe exit side thereof with a lining 23 of a material adapted to withstand intense Iheat, such for example as a high chrome refractory.

- 'I'he burners may extend through the floor 9 of the furnace and are adapted to direct the iiame upwardly in the combustion chambers i2 and i3.

The burners are preferably of suiicient length so that combustion beginswithin the burner and has reached a point at the exit of the burner such that a substantial amount of heat is available for the lower tubes within th combustion chambers. It is to be understood that a row of such burners extends longitudinally of each combustion chamber so as to apply heat uniformly along the tubes, to be described. The air ducts I6 may be omitted provided other means is provided to obtain the proper air supply for the burners. Obviously the burners may be of any other desired type, the above being given as an example only.

AThe furnace is also provided with a convection chamber 30 located above the combustion' chambers l2 and I3 and having a cross section substantially less than that of said combustion chambers. The convection chamber 30 is formed by side Walls 3l Which-are joined to the side walls l0, I0 by roof sections 32. The walls 3l and 32- thereof may be supported .in any convenient manner (not shown) as for example from a framework 3.3 of structural shapes which may be located externally of the furnace walls. A hood above described 34 is mounted over the walls 3l of the convection chamber 30 and may be supported by struc.- tural members 35, carried by the stays I4. The hood is adapted to direct gases from 'the convection chamber 30 to a stack` 36.

Disposed within the convection chamber 30 is a bank of convection tubes 40 connected for the passage of the uid being treated, for example oil, from the upper to the lower tubes of said bank. The side wall I0` and thecenter wall II of the combustion chamber I2 may be lined with sets of wall tubes 4I and 42 respectively, which extend longitudinally of the furnace and are sufficiently close to the path' of the llame to extract heattherefrom both by radiation and convection. The lower tubes may be mounted at a level corresponding to the zone at which combustion has progressed sufficiently to raise the flame to the required temperature for e'lcient heating.

The wall tubes 4I and 42 are closely spaced so as to substantially shield the walls of the combustion chamber I2 from the intense radiant heat of the flame. It is accordingly possible to construct the walls of a low grade refractory materialor of an insulating material. The walls mayv have a coating Illa, of insulating material on the outside so as to form a more effective seal. 'In certain' cases it may. be desirable to cast or form the walls monolithic in which case the insulating coating may be omitted as the walls themselves would then be gas tight.

Sets of side wall tubes 43 and center wall tubes 44 are located in the combustion chamber I3; in aposition to shield the walls I0' and Il ofisuid chamber and to receive heat by radiation and convection in a manner similar to tubes 4I and 42 above described. The tubes 43 and 44 maybe arranged inone or more layers as, for example, in two layers as illustrated in Fig. 1, so as to obtain the desired rate of heat transfer as for example, a rate suitable for soaking or maintaining the oil at a given temperature. A set of side wall tubes 45 may be mounted adjacent the side wall I0 above the tubes 43 so as to completely shield the upper .part of said side wall from the flame. f

It is to be understood that the various tubes may be supported in any convenient manner, as for example from the stays or structural members 35, the manner of support forming no part of the present invention.

The tubes above mentioned may be connected in various sequences, depending upon the use to which the furnace is to be applied and the nature of the fluid to be treated. In the example illustrated in Fig. 1, the fluid is supplied to the bank 40 of convection tubes from a line 46, is passed downwardly through the convection tubes'countercurrent to the path of the combustion gases, is thence supplied by a line 41 to the side wall tubes 4I, is passed downwardly through said tubes, thence through a line 48 to the center wall tubes 42, thence outwardly through a. line 49. Fluid may also be supplied through a line 50 to the side wall tubes 45 and may pass downwardly through said side wall tubes, thence through the side wall tubes 43, thence through a line 51to the center wall tubes 44, thence outwardly through a line 52. Provision is made by means of a pipe 53, controlled by a valve 54, to interconnect the lines 49 and 50 so as to permit the uid to fpass "directly from theV center `wall tubes42 tothe side wall tubes 45, and suitf able means, such as valves 55 and 55', maybe provided to close the external connections to the lines 49 and 50.

In the above described furnace, the side and center wall tubes are located sufficiently close to the path of flame so that they receive a substantial amount of heat by radiation and also are traversed by the combustion gases and absorb heat by convection therefrom. The flame is thus reduced in temperature before it reaches the tubes in the convection chamber 3| l to a point such that injury to the lower tubes in said chamber is prevented. The combustion gases, however, still contain a substantial amount of heat which is removed by the convection tubes 40 before the gases reach'the stack 3.6.

It is to be noted that the path of the gases from the burners 20 to the stack 36 is substantially vertical and without appreciable change in direction. By this construction the resistance to the flowof gases is reduced to a minimum and the necessity for a high, expensive stack is avoided.

The use of two combustion chambers I2 and I3 permits independent adjustment whereby the rate of heating, of the fluid may be controlled. For example, when used in an oil cracking plant preheating may occur in the convection chamber 3D, the oil may be furtherheated to cracking temperature in the wall tubes 4I and 42 of the combustion chamber I2 and may be maintained at that temperature for a substantial period of time in the wall tubes 43, 44 and 45` associated with the combustion chamber I3. In such case the combustion chamber I3 constitutes a soaking zone in which the oil is maintained at cracking temperature a predetermined length of time.

Itis obvious that various changes may be made in the direction of oil flow, the numbers of tubes in each set, the velocity in the different chambers and in the adjustment of the burners so as to heatthe oil in its passage through the furnace at predetermined rates adapted to obtain any desired temperature gradients.

In some instances the combustion chambers I2 and I3 may be used for different purposes. For example, the valve 54 may be closed and the valves 55 opened to make external lconnections to the lines 49 and 50 so that oil for cracking may be supplied through line 46, passed through the convection tubes 40 and through the wall tubes 4I and 42 of the combustion chamber I2 and out through line 49. Other oil, for example oil to be reformed, may be supplied to the furnace through the line 50 and passed through the tubes 43, 44 and 45 in the combustion chamber 'I3 and thence outwardly through the line 52. the rate of combustion being adusted to provide proper temperature control in each chamber.

In the case of a small plant it may be desirable tb operate the furnace at times as a cracking unit and at other times as a combination cracking and reforming u'nit. In such event, the above construction reduces the furnace cost and avoidsthe necessity for maintaining two furnaces.

In certain plants, the type of oil varies from time to time. The invention .provides means for adapting the furnace to use with such various types of oil by separatelyvcontrolling the rate of combustion in the two combustion chambers in accordance with the requirements in each particular case. A

Since the convection chamber is of smaller cross-section than the combustion chamber, the velocity of gases. ov er the tubes 44 is greater than the velocity over the wall tubes. The proportion can be made such, taking into consideration `the available heat and the desired rate of transfer, that the convection tubes and wall tubes' operate with maximum eiiiciency to extract heat from th'e combustion gases and the heating eect is distributed as desired between the various sets of tubes. In general, the increased velocity Icompensates for the lower heat content` of the gases in the convection chamber and increases the heat transfer to the convection tubes.

A simplied form of furnace is shown in Fig. 2

in which a single combustion chamber 59 is used in place of the two combustion chambers |2- and I3 of Fig. 1. l'I'he furnace in Fig. 2 comprises a floor 60 and a pair of side walls 6I forming the combustion chamber 59. Side walls 62, joined to the side walls 6l Iby roof sections 63, form a convection chamber 64. A'supporting framework 65, hood 66 and stack 6l may be arranged in the manner set forth in connection with Fig, l1. A row of burners 68, similar to the burners 20 above described, may be located in or near the oor 60 to direct the flame upwardly toward the stack 61. A bank of convection tubes 69 is located in the convection chamber 64 and thewalls 6| may Ibe lined by side wall tubes V'HL 'I'he wall tubes 'l0 may extend to a point opposite the tip of the burners 68 for the purpose to be described. In the operation of this furnace, a fluid such as oil may be supplied through a linell, may pass downwardly-through the convection tubes 69, thence through side wall tubes 10, and out through a line 12. The side wall, tubes 10 are located closely adjacent the path of the ame so as to receive heat by radiation and convection therefrom and to substantially reduce the temperature of the flame before the gases reach the convection tubes 69. i

The burner 68 is suiiiciently long so that combustion begins therein and heats a portion of the burner to radiance. 'I'he lower side wall tubes consequently receive heat by radiation from the burner and the tubes thereabove receive heat by radiation from the flame as it emerges from the burner and by convection from the combustion gases. The entire space within the combustion chamber is accordingly utilized efliciently for the transfer of heat from the fuel to thefluid within the tubes. l

This type of furnace is particularly adapted to oil cracking plants inasmuch as the oil is rst heated in the convection tubes 69 and is thereafter quickly raised to cracking temperature in the side wall tubes 1l). The arrangement may be such that certain of the tubes constitute a soaking section and maintain the oil at required temy peratures. Obviously,- the sidewall tubesA may be used in more than one layer if desired as illustrated in connection with the tubes 43 and 44 of Fig. 1.

Although a shecic type of furnace has been disclosed for purposes of illustration, it is obvious that various changes -and modifications may be made therein by a person skilled in the art without departing from the scope of-the present invention. The invention is only to be limited in accordance with the following claims when interpreted in view of the prior art.

Wh t is claimed is: A

1. two cell upshot oil cracking still comprising, in combination, side walls forming a rectangular furnace chamber, a central vertical 1ongitudinal wall in the lower part of said furnace chamber dividing 1said chamber into a pair of*v narrow vertical combustion chambers communieating at their upper parts above said center wall,

additional side walls located above said rst walls and oiset inwardly therefrom to form a conveccenter wall to receive gases equally from both tion chamber narrower than said furnace chamber located directly above and spaced from said combustion chambers, a hood above said convection chamber to receive combustion gases therefrom, a bank of horizontal convection tubes carv rying hydrocarbon oil substantially lling said convection chamber, vertical rows of horizontal side` wall radiant heat tubes adiacent said rst lside walls to shield the same from radiant heat and additional vertical rows of horizontal tubes y on both sides of said center wall to shield the same from radiant heat, said additional rows b terminating at the top of said center wall where- C by an unobstructed passage is provided from said wall, additional side walls located above said lrst walls and offset-inwardly therefrom to form a convection chamber narrower than said furnace chamber located directly above and spaced from said center wall to receive gases-equally from both combustion chambers, a hoodabove said convection chamber to receive combustion gases therefrom, supporting means for said side-walls and hood comprising a framework located entirely outside of said walls, said framework having vertical members adjacent to and supporting said rst walls, other vertical members supported thereby and located adjacent to and supporting said additional side walls and members supported by said rst vertical members and supporting said hood, a bank of horizontal convection tubes carrying hydrocarbon oil substantially filling said.

convection chamber, vertical rows of horizontal side `wall radiant heat tubes adjacent said rst side walls toshield the same from radiant heat and-additional vertical rows of horizontal tubes on both sides of said center wall toshield the same from radiant heat, said, additional rows terminating at the top of said center wall whereby an unobstructed passage is provided from said combustion chambers to said convection chamber, and a row of burners spaced longitudinally along -the bottom of each combustion chamber to direct a flame upwardly between said rows of side wall tubes ,toward said convection tubes.

RALPH M. PARSONS. 

